{-# LANGUAGE ExistentialQuantification  #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE LambdaCase                 #-}
{-# LANGUAGE NamedFieldPuns             #-}
{-# LANGUAGE NondecreasingIndentation   #-}
module Announcer
    ( Announcer
    , AnnounceKey
    , packAnnounceKey
    , unpackAnnounceKey
    , AnnounceMethod(..)
    , forkAnnouncer
    , stopAnnouncer
    , schedule
    , cancel
    ) where

import qualified Data.MinMaxPSQ as MM
import Data.Wrapper.PSQ         as PSQ
import InterruptibleDelay
import Network.Kademlia.Routing as R
import Network.Kademlia.Search

import Control.Concurrent.Lifted.Instrument
import Control.Concurrent.STM
import Control.Monad
import Data.ByteString                      (ByteString)
import qualified Data.ByteString.Char8      as Char8
import Data.Function
import Data.Hashable
import Data.Maybe
import Data.Time.Clock.POSIX

newtype AnnounceKey = AnnounceKey ByteString
 deriving (Hashable,Ord,Eq)

packAnnounceKey :: Announcer -> String -> STM AnnounceKey
packAnnounceKey _ = return . AnnounceKey . Char8.pack

unpackAnnounceKey :: AnnounceKey -> AnnounceKey -> STM String
unpackAnnounceKey _ (AnnounceKey bs) = return $ Char8.unpack bs

data ScheduledItem
    = forall r. ScheduledItem (AnnounceMethod r)
    | StopAnnouncer
    | NewAnnouncement (IO ()) (IO ()) POSIXTime
    | SearchFinished (IO ()) (IO ()) POSIXTime
    | Announce (IO ()) POSIXTime
    | DeleteAnnouncement

data Announcer = Announcer
    { scheduled       :: TVar (PSQ' AnnounceKey POSIXTime ScheduledItem)
    , announcerActive :: TVar Bool
    , interrutible    :: InterruptibleDelay
    }

scheduleImmediately :: Announcer -> AnnounceKey -> ScheduledItem -> STM ()
scheduleImmediately announcer k item
    = modifyTVar' (scheduled announcer) (PSQ.insert' k item 0)

stopAnnouncer :: Announcer -> IO ()
stopAnnouncer announcer = do
    atomically $ scheduleImmediately announcer (AnnounceKey "*stop*") StopAnnouncer
    interruptDelay (interrutible announcer)
    atomically $ readTVar (announcerActive announcer) >>= check . not

data AnnounceMethod r = forall nid ni addr tok a.
                        ( Show nid
                        , Hashable nid
                        , Hashable ni
                        , Ord addr
                        , Ord nid
                        , Ord ni
                        ) => AnnounceMethod
    { aSearch  :: Search nid addr tok ni r
    , aPublish :: r -> tok -> Maybe ni -> IO (Maybe a)
    , aBuckets :: TVar (R.BucketList ni)
    , aTarget  :: nid
    , aInterval :: POSIXTime
    }

schedule :: Announcer -> AnnounceKey -> AnnounceMethod r -> r -> IO ()
schedule announcer k AnnounceMethod{aSearch,aPublish,aBuckets,aTarget,aInterval} r = do
    st <- atomically $ newSearch aSearch aTarget []
    let announce = do -- publish to current search results
            is <- atomically $ do
                bs <- readTVar (searchInformant st {- :: TVar (MinMaxPSQ' ni nid tok -})
                return $ MM.toList bs
            forM_ is $ \(Binding ni tok _) -> do
            aPublish r tok (Just ni)
            return ()
        onResult _ = return True -- action for each search-hit (True = keep searching)
        search  = do -- thread to fork
            atomically $ reset aBuckets aSearch aTarget st
            searchLoop aSearch aTarget onResult st
            atomically $ scheduleImmediately announcer k
                         $ SearchFinished {- st -} search announce aInterval
            interruptDelay (interrutible announcer)
    atomically $ scheduleImmediately announcer k $ NewAnnouncement search announce aInterval
    interruptDelay (interrutible announcer)

cancel :: Announcer -> AnnounceKey -> AnnounceMethod r -> r -> IO ()
cancel announcer k _ _ = do
    atomically $ scheduleImmediately announcer k $ DeleteAnnouncement
    interruptDelay (interrutible announcer)

forkAnnouncer :: IO Announcer
forkAnnouncer = do
    delay <- interruptibleDelay
    announcer <- atomically $ Announcer <$> newTVar PSQ.empty
                                        <*> newTVar True
                                        <*> pure delay
    fork $ announceThread announcer
    return announcer


announceThread :: Announcer -> IO ()
announceThread announcer = do
    myThreadId >>= flip labelThread "announcer"
    fix $ \loop -> do
    join $ atomically $ do
        item <- maybe retry return =<< findMin <$> readTVar (scheduled announcer)
        return $ do
        now <- getPOSIXTime
        -- Is it time to do something?
        if (prio item < now)
            then do -- Yes.  Dequeue and handle this event.
                 action <- atomically $ do
                     modifyTVar' (scheduled announcer)
                                 (PSQ.delete (key item))
                     performScheduledItem announcer now item
                 -- Are we finished?
                 mapM_ (>> loop)  -- No? Okay, perform scheduled op and loop.
                       action
            else do -- No.  Wait a bit.
                 startDelay (interrutible announcer) (microseconds $ prio item - now)
                 loop
    -- We're done.  Let 'stopAnnouncer' know that it can stop blocking.
    atomically $ writeTVar (announcerActive announcer) False

performScheduledItem :: Announcer -> POSIXTime -> Binding' AnnounceKey POSIXTime ScheduledItem -> STM (Maybe (IO ()))
performScheduledItem announcer now = \case

    (Binding _ StopAnnouncer _) ->  return Nothing

    -- announcement started:
    (Binding k (NewAnnouncement search announce interval) _) -> do
        modifyTVar (scheduled announcer)
                   (PSQ.insert' k (Announce announce interval) (now + interval))
        return $ Just $ do
            fork search
            return ()

    -- announcement removed:
    (Binding k DeleteAnnouncement _) -> return $ Just $ return ()

    -- time for periodic announce:
    --   (re-)announce to the current known set of storing-nodes.
    --   TODO: If the search is finished, restart the search.
    (Binding k (Announce announce interval) _) -> do
        modifyTVar (scheduled announcer)
                   (PSQ.insert' k (Announce announce interval) (now + interval))
        return $ Just announce

    -- search finished:
    --   if any of the current storing-nodes set have not been
    --   announced to, announce to them.
    (Binding _ (SearchFinished {- st -} search announce interval) _) -> return $ Just $ return ()